1. Field of the Invention
The present invention relates to a phase difference detecting apparatus which is suitably applicable, for example, to an automatic focal point detecting device of a camera, and particularly relates to a phase difference detecting apparatus for performing operation processing for phase difference detection through analog signal processing.
2. Description of Related Art
A conventional phase difference detecting apparatus will be described in relation to an automatic focal point detecting device of a camera. A condenser lens, a separator lens and a phase difference detecting apparatus are positioned in order in the rear of a film equivalent plane located to the rear of an objective lens. The phase difference detecting apparatus is provided with a pair of image sensors constituted by CCDs, or the like, for photoelectrically converting a pair of subject images focused by the separator lens, and an operation circuit for operating on a phase difference between the pair of subject images on the basis of electric signals generated through the photoelectric conversion so as to judge the focus state.
That is, a signal B(k) to be operated on which is time-serially output from one of the image sensors and a signal R(k) to be operated on which is time-serially output from the other image sensor are subject to differential operation on the basis of the following equation (1) to thereby calculate values H(1), H(2) . . . H(l), so that the focus state and the quantity of focal displacement are detected on the basis of a distribution pattern of the correlative values. EQU H(l)=.vertline. B(k)-R(K+l-1) .vertline. (1)
where l is an integer not smaller than 1 which shows a quantity of relative movement between the signals B(K) and R(k).
In such a conventional phase difference detecting apparatus, however, there have been problems in that since operation is carried out through digital signal processing by using a micro-computer or the like, an expensive A/D converter and so on are required in order to perform high-speed and accurate operation. In addition, round off errors are produced due to limitation in the number of bits of the microcomputer or the like, for carrying out the operation and, as a result, the accuracy of the operation deteriorates. Further, computer programming for controlling the operation processing is large and as a result, a large memory capable of storing a great number of digital data is required.